1. Field of the Invention
The present invention relates to an image reading device, and in particular, to an image reading device which reads an original document or image by using a light source which illuminates the original and a light sensor which receives light from the original.
2. Description of the Related Art
There have been proposed various conventional devices in which a plurality of different types of color light are emitted from plural LEDs so as to illuminate an original, and the light reflected from the original is received, as light of a plurality of different wavelengths, by a CCD sensor. For example, Japanese Patent Application Laid-Open (JP-A) No. 10-32681 discloses a reading device in which d plurality of different color lights are successively emitted so as to illuminate an object to be copied, and the light reflected from the object to be copied is read synchronously with the emission of the respective color lights. Further, Japanese Patent Application Laid-Open (JP-A) No. 7-6197 discloses a device in which a bar code is illuminated by light emitted from respective LEDs of an LED array, the light reflected from the bar code is read at a CCD line sensor, and on the basis of the amounts of light received by the respective CCDs, the duties of the period of time that light is emitted from the respective LEDs corresponding to the CCDs are set such that the bar code is illuminated at a uniform and constant amount of light.
In devices such as those described above, in order for the CCD sensor to receive a desired amount of light, the charge accumulating times of the CCD sensor (times at which the CCD sensor can receive light, i.e., light receivable times) must be varied with the plural LEDs always emitting light, or the light emitting times of the plural LEDs must be controlled with the charge accumulating times of the CCDs fixed.
If a method is used in which only one of the charge accumulating times of the CCD sensor or the light emitting times of the LEDs are controlled, not only are there fewer degrees of freedom of control, but also, fine control cannot be effected.
The present invention was achieved in light of the aforementioned, an object thereof is to provide an image reading device in which the degrees of freedom of control at the time of reading are increased.
In order to achieve the above object, a first aspect of the present invention is an image reading device comprising: a light source which illuminates an original and which is formed by a plurality of light emitting elements which emit light of different wavelengths; one or more light sensors which receive light from the original and which are formed by a plurality of light receiving elements which receive light from the light source; and control means for controlling the light sensors by using a predetermined minimum charge accumulating time as a unit such that the light sensors receive light from the original during a light receivable time which is an integer multiple of the minimum charge accumulating time, and for controlling the respective light emitting elements such that the respective light emitting elements are pulse width modulated synchronously with the light receivable time and such that one period thereof equals the minimum charge accumulating time, and emit light. Light from the light source means both light transmitted through (passing through) the original and light reflected by the original.
In the light source relating to the present invention, a plurality of light emitting elements, which emit light of different wavelengths, are provided in a row, and the light source illuminates the original. In the plural light sensors, plural light receiving elements, which receive light of different wavelengths, are provided in a row, and the plural light sensors receive light from the original.
The control means controls the respective light sensors by using a predetermined minimum charge accumulating time as a unit such that the respective light sensors receive light during a light receivable time which is an integer multiple of the minimum charge accumulating time. The control means controls the respective light emitting elements such that the respective light emitting elements are pulse width modulated synchronously with the light receivable time and such that one period thereof equals the minimum charge accumulating time, and emit light.
By using the predetermined minimum charge accumulating time as a unit, the light sensors receive light from the original during a light receivable time which is an integer multiple of the minimum charge accumulating time. The respective light emitting elements are pulse width modulated synchronously with the light receivable time and such that one period thereof equals the minimum charge accumulating time, and emit light. Thus, the number of degrees of freedom in control at the time of reading can be increased, and fine control can be carried out.
On the basis of output from the plurality of light sensors in a state in which there is no original in a case in which transmitted light from the original is to be read, and on the basis of output from the plurality of light sensors when a reference plate of a predetermined color is set instead of the original in a case in which light reflected from the original is to be read, the control means may compute a target value of at least one of a light receivable time of each of the plurality of light sensors and a light emitting pulse width of each of the plurality of light emitting elements, such that color balance and light distribution of each of the plurality of light emitting elements fall within allowable ranges, and the control means may effect control such that the at least one of the light receivable time of each of the plurality of light sensors and the light emitting pulse width of each of the plurality of light emitting elements becomes the computed target value.
In this way, the control means computes a target value of at least one of a light receivable time of each of the plurality of light sensors and a light emitting pulse width of each of the plurality of light emitting elements, such that color balance and light distribution of each of the plurality of light emitting elements fall within allowable ranges, and the control means effects control such that the at least one of the light receivable time of each of the plurality of light sensors and the light emitting pulse width of each of the plurality of light emitting elements becomes the computed target value. Thus, light of a color balance and light distribution which fall within allowable ranges can be illuminated onto the original.
The control means may control the light receivable time of each of the plurality of light sensors and the light emitting pulse width of each of the plurality of light emitting elements, such that the amount of light received from the original by each of the plurality of light sensors becomes a desired amount of light received.
The control means computes a target value of at least one of the driving current of each of the plurality of light emitting elements, the light receivable time of each of the plurality of light sensors and the light emitting pulse width of each of the plurality of light emitting elements, such that color balance and light distribution of each of the plurality of light emitting elements fall within allowable ranges, and the control means effects control such that the at least one of the driving current of each of the plurality of light emitting elements, the light receivable time of each of the plurality of light sensors and the light emitting pulse width of each of the plurality of light emitting elements becomes the computed target value. Thus, the number of degrees of freedom in control at the time of reading can be increased even more, and even more fine control can be carried out.
The control means may control the light receivable time of each of the plurality of light sensors, the light emitting pulse width of each of the plurality of light emitting elements, and the driving current of each of the plurality of light emitting elements, such that the amount of light received from the original by each of the plurality of light sensors becomes a desired amount of light received.
The light source may be formed by the light emitting elements being arranged on a substrate, and the image reading device may further comprise: detecting means for detecting a temperature of the substrate; and temperature changing means for changing the temperature of the substrate, wherein on the basis of the temperature detected by the detecting means, the control means controls the temperature changing means such that the temperature of the substrate becomes a standard temperature. substrate, the temperature of the substrate can be made to be a reference temperature. Therefore, the LEDs can be maintained at the reference temperature. Thus, the LEDs can emit, at the same amount of emitted light, light of wavelengths at the time the LEDs are at the reference temperature.
Another aspect of the present invention is an image reading device comprising: a light source which illuminates an original document or image to be read and which is formed by a plurality of light emitting elements which emit light; a light sensor which receives light from the original; and control means for controlling a light receivable time and a turning on-and-off period such that the period for turning each light emitting element on and off is 1/n, n being an integer, of a predetermined minimum charge accumulating time and the light receivable time of the light sensor is a time which is greater than or equal to the minimum charge accumulating time and is an amount of time over which light, of an amount generated by a light emitting element being turned on a number of times which is an integer, can be received. In accordance with this aspect, both, on the one hand, the light receivable time of the light sensor, and, on the other hand, the period over which the light emitting elements are turned on and off and/or the light emitting pulse width, are controlled. Therefore, as compared with a case in which only the light receivable time is controlled or a case in which only at least one of the period for turning on and off the light emitting element and the light emitting pulse width is controlled, the number of degrees of freedom of control for receiving a predetermined amount of light is increased, and more fine control can be carried out. Further, the light receivable time means the time over which the light sensor is set in a light receivable state, e.g., the time over which the electronic shutter disposed between the light emitting elements and the light sensor is opened, i.e., the time over which charge can be accumulated. The minimum charge accumulating time is the minimum time over which the light receivable time can be controlled, e.g., the minimum time over which opening of the electronic shutter can be controlled.
In this aspect, the control means may compute a target value of at least one of the light receivable time of the light sensor and the light emitting pulse width of each of the light emitting elements, and control the light receivable time and the turning on-and-off period such that the at least one of the light receivable time of the light sensor and the light emitting pulse width of each of the light emitting elements becomes the computed target value.
In addition, the control means may be structured so as to be able to control the driving current to the light emitting elements.
Further, light emitting diodes (LEDs) may be used for the light emitting elements.